The present invention relates to a substrate for magnetic disks using a ceramic support.
Magnetic disks as storage media play a key role in the information processing systems with computer. In order to meet the recent demand for magnetic recording of higher density and greater storage capacity, recording media of smaller thickness and higher surface precision are being fabricated by thin-film techniques such as sputtering.
Substrates for magnetic recording media are conventionally made of aluminum alloys and have an anodized aluminum coat of a general thickness of about 2 .mu.m. This anodized aluminum coat provides an adequate hardness for the substrate surface, but due to the small thickness of this hard anodized aluminum layer and the difference in thermal expansion coefficient between the aluminum alloy and anodized aluminum, the dimensions of the substrate easily change as it is heated up. When a magnetic recording material is sputtered onto the substrate, sputtered ions or electrons impinge on the substrate and the resulting thermodynamic energy causes an increase in the substrate temperature. For coating with a mangetic recording material comprised of .gamma.-Fe.sub.2 O.sub.3 particles, the substrate is typically heated to 300.degree. C. or higher. In either case, the temperature elevation increases the chance of dimensional instability in the aluminum substrate. When high-density recording is attempted with a magnetic medium formed on such defective aluminum substrate, writing or reading errors are highly likely to occur.
A magnetic disk system consists of platters which are stacked in a pack and are rotated about a spindle at a high speed of 1000 to 3000 rpm for reading and writing data. A substrate made of an aluminum alloy is highly stretchable by centrifugal force and this also causes increased writing or reading error in high-density magnetic recording.
As a further disadvantage, the aluminum alloy substrate, although its surface is usually anodized, has no less than 100 voids of a size of 2 to 3 .mu.m over each side of the substrate of 5-inch diameter. These void defects are fatal to a high-density recording magnetic disk system and render accurate writing and reading impossible. Therefore, the development of a substrate for magnetic disks which has smaller void defect densities has long been a concern to the industry.